Seismic Geomorphology for Tidal Depositional Environment Interpretation, Late Oligocene Upper Gabus West Natuna Basin, Indonesia

The Late Oligocene Upper Gabus sandstone is known as one of the most productive hydrocarbon reservoirs in West Natuna Basin (WNB), Indonesia. The reservoir is characterized by thick sandstone unit (50 to 100 ft thick), generally form a dirtying upward succession. Vertical and lateral heterogeneities are observed mainly controlled by lateral facies change that introduces challenges in predicting reservoir distribution and connectivity.

An integrated geoscience study was conducted to comprehend the reservoir depositional system, geometry, and distribution. Detailed well correlation was performed, guided by seismic to maintain chronostratigraphic correlation, identifying sedimentological information that was linked towards the presence of lateral accretion, erosion or facies change within this reservoir. 3D seismic interpretation was performed to recognize sedimentological geometries and trends. The result displays clear development of estuarine type architectural elements such as longitudinal subtidal-bar complex, tidal and intertidal sinuous channel geometries. Reservoir Depositional Environment (RDE) map illustrates that series of longitudinal bar sandstones may have been extensively developed towards the east and northeast of study area separated by the intervening tidal channel heterolithics or shales. This kind of complex reservoir network might promote stratigraphic play of undrilled isolated reservoir potentials, albeit remaining risks related to reservoir presence and intra-formational seal capacity.